1. Field of the Invention
The present invention relates to an engine brake control device by which a loss of traction (hereinafter referred to as slippage) by a driven wheel is prevented during a reduction of a vehicle speed.
2. Description of the Related Art
A known engine brake control device comprises a vehicle speed detecting means for detecting the vehicle speed, an engine speed detecting means for detecting the engine speed, and a control means for feeding air into the engine when it is determined that slippage of a driven wheel has occurred during a reduction of a vehicle speed. Slippage of the driven wheel is considered to have occurred when it is determined that the engine speed detected by the engine speed detecting means is lower than a speed corresponding to the vehicle speed detected by the vehicle speed detecting means.
This engine brake control device is used to reduce an excessive engine braking force, and thus prevent slippage of the driven wheel, by feeding air into the engine when slippage of the driven wheel is caused by an excessive engine brake force produced, for example, by a rapid shift from a high gear to a low gear (refer to Japanese Unexamined Patent Publication No. 59-138750).
U.S. Pat. No. 3,802,528 discloses an arrangement for an automatic torque control, by which the degree of opening of the throttle valve is increased when such slippage occurs.
Generally, a fuel supply to the engine is stopped during a reduction of the vehicle speed, i.e., when the engine speed is higher than a predetermined value and the throttle valve is closed, so that a discharge of unburnt components of an exhausted gas is prevented and the fuel consumption is reduced.
In an engine provided with this prior art engine brake control device, air is fed into the engine when a slippage of the driven wheel occurs during a reduction of the vehicle speed. Nevertheless, when an excessive engine braking force is produced, for example, due to a rapid shift from a high to a low gear, the engine brake force can not be sufficiently reduced by only feeding air into the engine, and therefore, slippage of the driven wheel may still occur when the above prior art device is used.